The present invention relates to aggressive wound therapy devices, and more particularly to vacuum wound therapy devices. Even more particularly the invention relates to controlling the vacuum applied by vacuum wound therapy devices.
Medical professionals, such as nurses and doctors, routinely treat patients having surface wounds of varying size, shape, and severity. Aggressive wound therapy, as opposed to passive wound therapy, takes advantage of environmental modifications to actively induce healing. It is known that controlling the topical atmosphere adjacent a wound can enhance the healing process. Several aggressive wound therapy strategies are known including hyperbaric therapy, thermal therapy and negative pressure therapy.
In negative pressure therapy, a wound bed is subjected to an air pressure lower than the ambient air pressure. Applying a negative pressure or vacuum to a wound draws out exudate, which might contain dirt and bacteria, from the wound to further promote healing. Some dressings include an apparatus attached thereto for applying a vacuum through the bandage to the wound to draw exudate and promote healing. However, it has been found that rapid changes in negative pressure levels applied to open wounds (chronic wounds) can cause discomfort to patients.
It is also known to use a vacuum treatment bandage for accelerating wound healing. A vacuum bandage is a bandage having a cover for sealing about the outer perimeter of the wound and under which a vacuum is established to act on the wound surface. This vacuum applied to the wound surface accelerates healing of chronic wounds. Typically, suction tubes are provided for drawing exudate away from the wound, and the suction tubes may be used to create the vacuum under the cover. If the cover is a flexible cover, which is typically more comfortable for the patient, a porous packing may be provided under the cover to provide the space in which the vacuum is formed. Additionally, it is known a heater within a wound treatment apparatus to promote healing. The following U.S. Patents establish the nature of vacuum and/or heat treatment bandages and devices: U.S. Pat. Nos. 6,095,992, 6,080,189, 6,071,304, 5,645,081, 5,636,643, 5,358,494, 5,298,015, 4,969,880, 4,655,754, 4,569,674, 4,382,441, and 4,112,947. All of such references are incorporated herein by reference for purposes of disclosing the nature of such vacuum or heat treatment of wounds.
As shown, for example, in U.S. Pat. No. 5,645,081 (hereinafter the '081 patent), a method of treating tissue damage is provided by applying negative pressure to a wound. The negative pressure is provided in sufficient duration and magnitude to promote tissue migration in order to facilitate the closure of the wound. FIG. 1 of the '081 patent discloses an open cell polyester foam section covering the wound, a flexible hollow tube inserted into the foam section at one end and attached to a vacuum pump at another end, an adhesive sheet overlying the foam section, and tubing to adhere to the skin surrounding the wound in order to form a seal that allows the creation of a vacuum when the suction pump is operating. The '081 patent further teaches use of negative pressure between about 0.1 and 0.99 atmospheres, and that the pressure can be substantially continuous, wherein the pressure is relieved only to change the dressing on the wound. Alternatively, the '081 patent teaches use of a cyclic application of pressure in alternating periods of application and nonapplication. In a preferred embodiment, pressure is applied in 5-minute periods of application and non-application.
The following pending applications, assigned to the same assignee as the present application is licensed, are also specifically incorporated herein by reference: U.S. patent application Ser. No. 09/369,113 filed Aug. 5, 1999 and titled Wound Treatment Apparatus, U.S. patent application Ser. No. 09/725,352 filed Nov. 29, 2000 (Publication No. US-2002-0065494-A1 published May 30, 2002) and titled Vacuum Therapy and Cleansing Dressing for Wounds, and U.S. patent application Ser. No. 09/725,666 filed Nov. 29, 2000 and titled Wound Treatment Apparatus.
Various prior art references teach the value of the vacuum bandage or the provision of vacuum to the surface of a chronic wound. Several Russian language articles exist that establish the efficacy of vacuum therapy. Examples of such prior art articles, each of which discusses the use of application of vacuum to a wound to promote healing, are as follows: Vacuum therapy in the treatment of acute suppurative diseases of soft tissues and suppurative wound, Davydov, et al. Vestn. Khir., September 1988 (“the September 1988 article”); Pathenogenic mechanism of the effect of vacuum therapy on the course of the wound process, Davydov, et al. Khirurigiia, June 1990 (“the June 1990 article”); and Vacuum therapy in the treatment of suppurative lactation mastitis, Davydov, et al., Vestn. Khir., November 1986 (“the November 1986 article”).
The Russian articles distinguish wound drainage from use of vacuum therapy for healing, and they report that vacuum therapy results in faster cleansing of the wound and more rapid detoxification than with the traditional incision-drainage method. The November 1986 article describes the vacuum therapy protocol as 0.8–1.0 atmosphere for 20 minutes at the time of surgery, and subsequent 1.5 to 3 hour treatments at a vacuum of 0.1 to 0.15 atmosphere, twice daily. These Russian articles teach that use of negative pressure accelerates healing. The Russian articles further teach using this vacuum method to decrease the number of microbes in the wound. The June 1990 article teaches that vacuum therapy provides a significant antibacterial effect. The June 1990 article describes the stepped up inflow of blood to the zone around the wound, which leads to an increase in the number of leukocytes reaching the focus of inflamation. Moreover, the Russian articles teach improvement of local blood circulation using vacuum therapy. The September 1988 article teaches improved inflow of blood into the wound zone, which intensifies the repair processes. The June 1990 article teaches that vacuum therapy promotes mobilization of blood plasma, intertissue fluid, and lymph into the wound. The June 1990 article reports that cellular and non-cellular elements of connective tissue appear twice as quickly in wounds treated with vacuum therapy. Subsequent articles and patents further develop the benefits obtained with vacuum therapy. The prior art, therefore, teaches the benefit and value of a vacuum bandage.